Polarization- and frequency-tunable microwave circuit for selective excitation of nitrogen-vacancy spins in diamond Johannes Herrmann, 1 Marc A. Appleton, 1 Kento Sasaki, 1 Yasuaki Monnai, 1 Tokuyuki Teraji, 2 Kohei M. Itoh, 1,3,a) and Eisuke Abe 3,b) 1 School of Fundamental Science and Technology, Keio University, 3-14-1 Hiyoshi, Kohoku-ku, Yokohama 223-8522, Japan 2 National Institute for Materials Science, 1-1 Namiki, Tsukuba, Ibaraki 305-0044, Japan 3 Spintronics Research Center, Keio University, 3-14-1 Hiyoshi, Kohoku-ku, Yokohama 223-8522, Japan (Received 13 September 2016; accepted 27 October 2016; published online 3 November 2016) We report on a planar microwave resonator providing arbitrarily polarized oscillating magnetic fields that enable selective excitation of the electronic spins of nitrogen-vacancy centers in dia- mond. The polarization plane is parallel to the surface of diamond, which makes the resonator fully compatible with (111)-oriented diamond. The field distribution is spatially uniform in a circular area with a diameter of 4 mm, and a near-perfect circular polarization is achieved. We also demon- strate that the original resonance frequency of 2.8 GHz can be varied in the range of 2–3.2 GHz by introducing varactor diodes that serve as variable capacitors. Published by AIP Publishing. [http://dx.doi.org/10.1063/1.4967378] In recent years, the nitrogen-vacancy (NV) center in dia- mond has emerged as a promising platform for quantum information processing and nanoscale metrology. 1–7 At the heart of both technologies lies an exquisite control of the NV electronic spin. 8 The ground state of the negatively charged NV center is an S ¼ 1 spin triplet with the m S ¼ 61 sublevels lying D gs ¼ 2.87 GHz above the m S ¼ 0 sublevel under zero magnetic field. The external static magnetic field B dc applied parallel to the quantization axis n NV (along one of the h111i crystallographic axes) further splits the m S ¼ 61 levels by 2 cB dc , with c ¼ 28 GHz/T being the gyromagnetic ratio of the NV electronic spin [see Fig. 1]. Initialization, control, and readout of this three-level V system are accomplished by an optically detected magnetic resonance (ODMR) technique, in which optical pumping by a green (500 nm) laser serves to initialize and read out the NV spin and short pulses of oscillating magnetic fields B ac (2.87 GHz) drive it into an arbitrary quantum-mechanical superposition. In ideal magnetic resonance experiments, B ac and B dc (k n NV ) should be orthogonal, 9,10 whereas in reality the direction of B ac at the location of the target NV center is hard to control or even know about. This is because a metal wire or a microfabricated stripline, commonly used for experiments with NV centers, generates B ac that is highly dependent on the positions. Moreover, B ac from these sources is linearly polarized, while the NV spin has clear transition selection rules; The m S ¼ 0 $ 1 (–1) transition is driven by r þ (r ) circularly polarized fields. To fully exploit the S ¼ 1 nature of the NV spin for quantum information and metrology applications, 11–14 it is highly desired to have a reliable means to generate arbitrarily polarized microwave fields. A few configurations for polarization-controlled B ac have been adopted for the NV system. A popular one is a pair of crisscrossed striplines, which generates desired fields only beneath the crossing point. 15,16 A pair of parallel striplines may be a simpler alternative. 17 In both examples, however, it is not straightforward to make the polarization plane perpendicular to n NV and thus to B dc . In this paper, we present yet another simple planar resonator circuit providing spatially uniform, arbitrarily polarized, and in-plane microwave magnetic fields. With a (111)-oriented diamond and B dc applied perpendicular to the diamond surface, both B dc ? B ac and n NV ? B ac are readily realized. This results in near-perfect selective excitation of the NV spin. In (111)-oriented synthetic diamond, it has been reported that the NV centers can be preferentially oriented along the [111] crystallographic axis. 18–21 Attracting enor- mous attention, such a special diamond substrate will lead to enhanced sensitivity in metrology as well as atomically pre- cise quantum information devices. Our resonator circuit design will be fully compatible with these applications. Figure 2(a) is a photograph of the fabricated microwave circuit consisting of a ring cavity connected to four stri- plines. The cavity is also loaded with four 1.1-pF capacitors. To establish electrical contacts between the capacitors and the ground plane on the back side, four via holes are manu- factured. The circular structure and the four symmetrically distributed capacitors form a microwave resonator, allowing a high magnetic field amplitude. Only Ports 1 and 2 are used FIG. 1. (Left) Schematic of the NV center. (Right) Energy levels of the neg- atively charged NV center with the static magnetic field B dc applied along the quantization axis n NV . a) Electronic mail: [email protected]b) Electronic mail: [email protected]0003-6951/2016/109(18)/183111/4/$30.00 Published by AIP Publishing. 109, 183111-1 APPLIED PHYSICS LETTERS 109, 183111 (2016)
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Polarization- and frequency-tunable microwave circuit for selectiveexcitation of nitrogen-vacancy spins in diamond
Johannes Herrmann,1 Marc A. Appleton,1 Kento Sasaki,1 Yasuaki Monnai,1
Tokuyuki Teraji,2 Kohei M. Itoh,1,3,a) and Eisuke Abe3,b)
1School of Fundamental Science and Technology, Keio University, 3-14-1 Hiyoshi, Kohoku-ku,Yokohama 223-8522, Japan2National Institute for Materials Science, 1-1 Namiki, Tsukuba, Ibaraki 305-0044, Japan3Spintronics Research Center, Keio University, 3-14-1 Hiyoshi, Kohoku-ku, Yokohama 223-8522, Japan
(Received 13 September 2016; accepted 27 October 2016; published online 3 November 2016)
We report on a planar microwave resonator providing arbitrarily polarized oscillating magnetic
fields that enable selective excitation of the electronic spins of nitrogen-vacancy centers in dia-
mond. The polarization plane is parallel to the surface of diamond, which makes the resonator fully
compatible with (111)-oriented diamond. The field distribution is spatially uniform in a circular
area with a diameter of 4 mm, and a near-perfect circular polarization is achieved. We also demon-
strate that the original resonance frequency of 2.8 GHz can be varied in the range of 2–3.2 GHz by
introducing varactor diodes that serve as variable capacitors. Published by AIP Publishing.[http://dx.doi.org/10.1063/1.4967378]
In recent years, the nitrogen-vacancy (NV) center in dia-
mond has emerged as a promising platform for quantum
information processing and nanoscale metrology.1–7 At the
heart of both technologies lies an exquisite control of the NV
electronic spin.8 The ground state of the negatively charged
NV center is an S¼ 1 spin triplet with the mS¼61 sublevels
lying Dgs¼ 2.87 GHz above the mS¼ 0 sublevel under zero
magnetic field. The external static magnetic field Bdc applied
parallel to the quantization axis nNV (along one of the h111icrystallographic axes) further splits the mS¼61 levels by 2
cBdc, with c¼ 28 GHz/T being the gyromagnetic ratio of the
NV electronic spin [see Fig. 1].
Initialization, control, and readout of this three-level V
system are accomplished by an optically detected magnetic
resonance (ODMR) technique, in which optical pumping by
a green (�500 nm) laser serves to initialize and read out the
NV spin and short pulses of oscillating magnetic fields Bac
(�2.87 GHz) drive it into an arbitrary quantum-mechanical
superposition. In ideal magnetic resonance experiments, Bac
and Bdc (k nNV) should be orthogonal,9,10 whereas in reality
the direction of Bac at the location of the target NV center is
hard to control or even know about. This is because a metal
wire or a microfabricated stripline, commonly used for
experiments with NV centers, generates Bac that is highly
dependent on the positions. Moreover, Bac from these sources
is linearly polarized, while the NV spin has clear transition
selection rules; The mS¼ 0 $ 1 (–1) transition is driven by
rþ (r�) circularly polarized fields. To fully exploit the S¼ 1
nature of the NV spin for quantum information and metrology
applications,11–14 it is highly desired to have a reliable means
to generate arbitrarily polarized microwave fields.
A few configurations for polarization-controlled Bac
have been adopted for the NV system. A popular one is
a pair of crisscrossed striplines, which generates desired
fields only beneath the crossing point.15,16 A pair of parallel
striplines may be a simpler alternative.17 In both examples,
however, it is not straightforward to make the polarization
plane perpendicular to nNV and thus to Bdc.
In this paper, we present yet another simple planar
in-plane oscillating magnetic fields in a wide range of fre-
quencies. Combined with a (111)-oriented diamond sub-
strate, near-perfect polarization control has been achieved.
In principle, our resonator design is not limited to the NV
centers and applicable to other spin-carrying color centers
and quantum dots in semiconductors compatible with
ODMR.2,25 We expect that the design presented in this
work, thus, will be useful not only for advanced study of
NV centers in diamond for quantum information and
metrology applications but also for a wide range of mag-
netic resonance experiments.
K.M.I. acknowledges the support from KAKENHI (S) No.
26220602, JST Development of Systems and Technologies for
Advanced Measurement and Analysis (SENTAN), JSPS Core-
to-Core Program, and Spintronics Research Network of Japan
(Spin-RNJ).
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183111-4 Herrmann et al. Appl. Phys. Lett. 109, 183111 (2016)